Buoyancy is the force that enables a swimmer to float even though then aren't moving
The upward force is the result of the pressure beneath the swimmer being greater than the pressure above them, allowing them to float
Fat is less dense than muscle in water, therefore more muscular people struggle to float
Need to maintain streamline, which minimises drag so the swimmer floats more efficently
Specialised swimsuits and buoyancy aids can enhance a swimmer's buoyancy as wetsuits reduce drag in open water